OBJECTIVES: 1) Identification of an unknown disulfide in the urine of a mentally retarded patient. 2) Dietary treatment of patients with hyperornithine and associated gyrate atrophy of the choroid and retina. 3) Study of a patient with pipecolic acidemia. 4) Biochemical and clinical evaluation of treatment for patients with argininosuccinic acidemia, maple syrup disease, homocystine, and methylmalonic acidemia.